This invention relates to a method for producing silicon nitride films and to a process for fabricating semiconductor devices using said method.
When the fabrication of silicon nitride film is carried out by the generally known low-pressure chemical vapor deposition (LPCVD) procedure using ammonia (NH3) and a silicon source such as dichlorosilane (SiH2Cl2), tetrachlorosilane (SiCl4), or hexachlorodisilane (Si2Cl6), a substantial deterioration in leakage characteristics and wet etching resistance is noted when the film production temperature declines below, for example, 600° C. It is thought that the generation of silicon-nitrogen bonds by reaction between the silicon source and nitrogen source is not promoted in such a low-temperature film-formation process and that the resulting occurrence of a large number of silicon dangling bonds in the silicon nitride film causes the deterioration in film quality.
The use of monomethylamine (CH3NH2) as a nitrogen source in place of ammonia (NH3) is described in Yasui, et al., Appl. Phys. Lett. 56(10), 5 Mar. 1990, p. 898-900, “Amorphous SiN films grown by hot-filament chemical vapor deposition using monomethylamine”, with the goal of improving silicon nitride film quality. This article concerns an evaluation of silicon nitride film formation at 600-800° C. by hot-filament CVD and thermal CVD using monosilane (SiH4) as the silicon source and monomethylamine (CH3NH2) as the nitrogen source. Monomethylamine (CH3NH2) was selected for the nitrogen source in this study because the decomposition energy of monomethylamine (CH3NH2) is, at 3.4 eV (CH3NH2), less than the 4.48 eV (NH2—H) of ammonia (NH3). The result was a reduction in the hydrogen concentration in the film to ≦1×1021 cm−3 at a film-formation temperature of 600° C.
JP 2002-009072 describes a method for forming silicon nitride films at 400-650° C. by LPCVD using trimethylamine ((CH3)3N, an amine-type gas) for the nitrogen source and a silane-type gas. However, this method requires that the trimethylamine ((CH3)3N) be preheated to 500-700° C. due to its high heat capacity. It is also stated that an insufficiently nitridated silicon nitride film (refractive index: RI=2.9) is obtained when silicon nitride film production is carried out, for example, at 550° C., without this preheating.
Yasui et al., Appl. Phys. Lett. 56(10), 5 Mar. 1990, p. 898-900, “Amorphous SiN films grown by hot-filament chemical vapor deposition using monomethylamine”
Japanese Laid Open (Unexamined or Kokai or A) Patent Application Number 2002-009072.
The silicon nitride films produced by LPCVD exhibit a very good coverage ratio and are broadly utilized in the fabrication of transistors (MOSFETs, etc.). However, their film properties undergo deterioration (deterioration in leakage properties, increase in impurities, etc.) when their production temperature is lowered for the purpose of reducing the thermal effects on the semiconductor device.
For example, when low-temperature silicon nitride film is produced by LPCVD using ammonia (NH3) and a silicon source such as hexachlorodisilane (Si2Cl6), the lower film-fabrication temperatures are accompanied by a deterioration in leakage properties, a deterioration in the wet etching resistance, and a substantial increase in the levels of hydrogen (H) and chlorine (Cl) in the film. It is thought that the generation of silicon-nitrogen bonds by reaction between the silicon source and nitrogen source is not promoted in the low-temperature film-formation process (for example, ≦600° C.) and that the resulting presence of a large number of silicon dangling bonds in the silicon nitride film is a cause of the deterioration in film quality.
In order to realize even lower thermal budgets when silicon nitride film is used for the sidewall film formed on the sidewall of the gate electrode of a semiconductor device or is used as the liner film elaborated prior to production of the interlayer dielectric film, a method is required that can produce high-quality silicon nitride film at high coverage ratios at film-formation temperatures ≦500° C., for example, at 450° C. However, issues with regard to a reduced electrical reliability by the semiconductor device are created by the deterioration in leakage characteristics and other problems that accompany lower film-formation temperatures.
Silicon nitride film production at a film-formation temperature ≦600° C. is not accomplished in Yasui, et al. With regard to JP 2002-009072, due to the use of trimethylamine, the required film properties cannot be obtained without preheating the gas.